Is there a way to make the scale an actual representation of the measure system (metric) I use?
If you set up a unit scale for Blender, inputs will parse the strings you enter in any field which expects length.

Supposing you have set the units to meters, and the Unit Scale to .5 (at least, in my build)..


If you enter '1', Blender will always interpret that as 1 Blender Unit (50cm)
If you enter '1m' Blender will interpret that as 1 meter
You can enter '25cm' or '250mm' or '.25m' etc. to refer to that length
If you enter '1in' Blender will interpret that as 1 inch. Because you have declared your dimensions to be in meters, that will be translated to 2.54cm
You can even enter an expression like '25m / 4' to get 6.25 meters


I'm open to correction, but it is true that the last-used radius for object creation can not be made to persist in the .blend file, and reverts to 1 of your declared base unit when you reopen it. However, the last creation size requested (in the tool region) does persist within sessions, on a per-primitive basis.

These are deliberate choices on the part of the developers, not careless. There are many choices in Blender that I don't personally agree with, but in the vast majority of cases, if I stop to think about them, I can see the arguments for the choices having been made that way. Usually it's to do with 'cleanliness'.. i.e. consistency between different parts of what is, after all,  a large application. I have been pleasantly surprised by that consistency in Blender's way of thinking, compared to many proprietary applications, especially those with a long history of accretions .. :)